In recent years, a cab structure is used that is composed of a hollow pipe member as a pole member of a cab installed on a construction machine.
In this type of cab structure installed on a construction machine, the pipe used as the pole member is required to have at least certain strength. However, if the thickness of pipe is increased to improve the strength, material cost and processing cost will increase. This results in high cost. For this reason, there is a need for a reinforcement structure for a pipe capable of solving problems in both strength and cost.
For example, Japanese Patent Laid-Open Publication TOKUKAI No. 2006-240568 discloses a structure that, in order to make up for a strength shortage of a pillar (pole member) that is composed of joined sheet metal members, has a plate member that is arranged inside the pillar from the top end to the bottom end of the pillar.
In addition, Japanese Patent Laid-Open Publication TOKUKAI No. 2005-111557 discloses a double-structured tube production method that includes a diameter reduction process for reducing the external peripheral length of an outer pipe after an inner pipe is inserted into the outer pipe whereby forming a double-structured tube to reinforce the pipes.